feat(ui/graph): optimize graph dynamics, immersive reader, and code blocks

- Fix #16: Implement D3.js transitions and active state badges for Knowledge Graph.
- Fix #12: Implement Immersive Reader Layout with Merriweather typography.
- Fix #20: Professional code block styling with high contrast and monospace fonts.
- Resolve DI runtime error in WASM by adding dummy services.
- Replace generic 'Not Found' message with Nexus preloader.
- Enforce 'no async void' architecture across UI services.

.agent/skills/nexus-architecture-standards/SKILL.md

@@ -29,9 +29,12 @@ This skill defines the architectural guardrails for the NexusReader project to e
 - Use `FluentResults` (`Result<T>`) for all Application services and handlers.
 - Avoid throwing exceptions for expected business failures; use `Result.Fail()`.
 
-### 4. MediatR Patterns
-- **Queries**: Read-only operations. Should return `Result<T>`. Use `AsNoTracking()` in EF Core.
 - **Commands**: State-changing operations. Should return `Result` or `Result<T>`.
++
++### 5. Async Operations (Zero Tolerance for `async void`)
++- All asynchronous operations MUST return `Task` or `ValueTask`.
++- Event handlers MUST use `Func<Task>` or async-compatible patterns.
++- UI components MUST await all service calls and use `InvokeAsync(StateHasChanged)` for state updates within async contexts.
 
 ## Audit Scripts
 - [ArchCheck.sh](scripts/arch_check.sh): A shell script to scan for illegal cross-layer imports.

.agent/skills/nexus-graph-d3/SKILL.md

@@ -8,4 +8,7 @@ description: D3.js standards for Knowledge Graph
 - **JS Interop:** Use ES6 modules and `IJSObjectReference`.
 - **Responsiveness:** SVG must use `viewBox` for fluid portrait scaling.
 - **Visuals:** Use CSS variables (`--nexus-neon`) for node styling.
+- **Transitions:** Enforce smooth 500ms transitions using the D3.js General Update Pattern (`.join()`).
+- **Animations:** Implement "Neon Flash" entry animations for newly discovered knowledge nodes.
+- **Contextual Highlight:** Support node/link dimming to emphasize the current reading context.
 - **Events:** JS emits events (like `nodeClicked`) caught by Blazor via `DotNetObjectReference`.

.agent/skills/nexus-ui-engine/SKILL.md

@@ -22,7 +22,7 @@ description: Design System & Component rules for Blazor
     - Light Mode: `--nexus-bg` (`#f8f9fa`), `--nexus-card` (`#ffffff`).
   - **Typography:**
     - UI Elements: `Inter` (Sans-Serif) for controls, menus, and labels.
-    - Reading Content: `Merriweather` (Serif) for books and articles to ensure high readability.
+    - Reading Content: `Merriweather` (Serif) with `line-height: 1.65` and `letter-spacing: -0.01em` for high readability.
   - **Effects:**
     - Subtle neon glows (`box-shadow: 0 0 15px rgba(0, 255, 153, 0.3)`).
     - Glassmorphism for overlays and modals.
@@ -30,6 +30,11 @@ description: Design System & Component rules for Blazor
 - **Adaptive Layouts:**
   - Support `.platform-mobile` and `.platform-desktop` context classes.
   - Handle safe-area insets (`--safe-area-inset-*`) for mobile devices.
+  - **Immersive Reader (Zen Mode):**
+    - Centered content flow: `max-width: 800px`, `margin: 0 auto`.
+    - Paper-white background: `#F9F9F9` for light mode reader canvas.
+    - Dedicated Scrollbars: Custom styled, thin scrollbars with `--nexus-neon` accents.
+    - Reachability: Large `padding-bottom` (e.g., `15rem`) to ensure comfortable reading of end-of-page content.
 
 - **Accessibility (A11y):**
   - Touch Targets: Min `44x44px` on mobile (enforced via CSS variables).